Anatomy of Lacrimal Apparatus made insanely easy

Whenever I used to read about the anatomy of the lacrimal apparatus, it had me in tears, but I wont let that happen to you. Join me as we unravel the anatomic details of this eye-watering wonder in a way that’ll keep you engaged and you would surely start loving ophthalmic anatomy .

Table of Contents

By the end of this article, you’ll understand the anatomy of lacrimal apparatus like never before and be able to impress your friends with your newfound knowledge. In this article, we shall read about the lacrimal apparatus and develop an in-depth understanding of its anatomy and clinical aspects.

What is lacrimal Apparatus?

Comprises structures concerned with tear formation and tear drainage

What are components of lacrimal apparatus

The primary components of the lacrimal apparatus, which include:
- The lacrimal gland and the accessory lacrimal gland
- The lacrimal puncta
- The canaliculi
- The lacrimal sac
- The nasolacrimal duct

Let us talk about each of these components one by one

What is LACRIMAL GLAND ?

The lacrimal gland is of the size of an almond measuring approximately 2 x 1.2 x 0.5 cm. It is situated in a depression present in the superolateral aspect of the orbit known as the lacrimal fossa.

The anterior part of the lacrimal gland is divided into two lobes by the anterior extention of the levator aponeurosis as it travels from its origin from the apex of the orbit. As it reached the lacrimal gland it splits it into two parts. The superior orbital lobe and an inferior palpebral lobe as can be seen in the diagram.

However the two lobes remain attached in the posterior part of the gland.

CLINICAL NUGGETS

When the upper lid is everted the PALPEBRAL lobe can be see through conjunctiva

Enlargement of the lacrimal gland pushes the eyeball medially and inferiorly. This is called INFEROMEDIAL DYSTOPIA

Lets talk about the ducts through which tears produced by the lacrimal gland reaches the conjunctiva

• About 10-12 ducts open in lateral part of superior fornix
•About 1-2 ducts open in lateral part of inferior fornix.

Moreover all the ducts opening in the superior fornix pass through the palpebral lobe. Therefore, excision of the palpebral lobe alone amounts to excision of the entire gland as far as the SECRETORY FUNCTION of the gland is concerned.

HISTOLOGY OF LACRIMAL GLAND

The lacrimal gland is a compound tubuloalveolar gland. It is made up of many lobules separated by connective tissue . Each lobule contains many acini. Each acini composed of large serous cells which, produce a watery serous secretion. It is structurally very similar to the parotid gland

What are ACCESSORY LACRIMAL GLAND ?

The accesory lacrimal glands are namely as follows–>

GLANDS OF KRAUSE
GLANDS OF WOLFRING
RUDIMENTARY LACRIMAL GLANDS ( caruncle , plica semilunaris )

All together contribute to BASAL TEAR SECRETION despite forming only 10% of total lacrimal secretory mass.

STRUCTURES ASSOCIATED WITH TEAR TRANSPORT

What is a LACRIMAL PUNCTA?

Lacrimal puncta are openings one each in the upper eyelid( upper lacrimal puncta) and the lower eyelid (lower lacrimal puncta).They are located at the posterior edge of the lid margin at the junction of the lash-bearing lateral five-sixths (PARS CILIARIS) and the medial non-ciliated one-sixth (PARS LACRIMALIS).

Each punctum sits on the lacrimal mound known as PAPILLA LACRIMALIS or LACRIMAL PAPILLA. As this is avascular the lacrimal mound looks pale in appearance. Increased paleness helps us identify and is often a clue to underlying punctal stenosis

Normally they face slightly posteriorly and can be inspected by everting the medial aspect of the lids. Upper punctum is 6 mm from inner canthus. The lower punctum is situated 6.5 mm from inner canthus. therefore clearly the lower punctum is laterally situated to the upper punctum.

The location of the puncta and its patency is of utmost importance. For example in punctal stenosis and blockage of the punctum with the eyelash, the patency is lost leading to blockage in the entry of tears into the lacrimal apparatus. Similarly in cases of ectropion or due to a large caruncle, the punctum sometimes gets displaced from its original position.

What is a LACRIMAL CANALICULUS ?

Th lacrimal canaliculus are a connection between the punctum and the lacrimal sac. We have a superior and an inferior canaliculus corresponding to a superior and an inferior punctum. Each canaliculus is about 0.5 mm in thickness .Each canaliculus has a vertical part (2cm) and a horizontal part (8cm). The junction of the two parts is called as an AMPULLA .

90%-10% RULE

In more than 90 % of population the two canaliculi unite to form the common canaliculus.
A Small diverticulum/ dilatation is present just before the common canaliculus opening into the lacrimal sac. this is called the LACRIMAL SAC OF MAIER.
The opening of the common canaliculus is present at about 2.5 mm below the apex of lacrimal sac
In 10 % of population each canaliculus opens separately into the sac.

There are some angles that one must remember .The two canaliculi form an angle of about 57 to 65 degrees at the common canaliculus. Also the common canaliculus inserts into the lacrimal sac at an angle to prevent regurgitation of the fluid straight away from the sac to the canalicular system. this angle is about 58-90 degrees.A clinical point to note here is that if the this angles becomes more obtuse there is an increased possibility of the patient to develop dacryocystitis .

The common canaliculus opens into the lacrimal sac. A small flap of mucosa overhangs the junction of the common canaliculus and the lacrimal sac. This is called the valve of Rosenmuller .It prevents reflux of tears into the canaliculi.

HISTOLOGY OF LACRIMAL CANALICULUS

The canaliculi are made of three layers :-

Epithelium : stratified squamous >10 layers of cells
Corium : elastic tissue
Pars lacrimalis : fibres of orbicularis surrounding the corium that have a sphincter like arrangement

Although the thickness of canaliculus is mere is 0.5 mm, it can be dilated upto 2-3 mm because of the presence of the elastic tissue( corium) in its wall. For detailed anatomical relations of the canaliculi , refer to the video on “anatomy of lacrimal apparatus“

What is LACRIMAL SAC ?

The common canaliculus opens into a samll sac called the lacrimal sac .The lacrimal sac is 10–12 mm long. It has 3 parts:-

Fundus : portion of the sac above the opening of common canaliculus
Body : middle part of sac
Neck : narrow small part that continues into the naso-lacrimal duct

LOCATION OF THE LACRIMAL SAC :- the lacrimal sac is situated in the fossa for the lacrimal sac. This is formed by the frontal process of the maxillary bone and the lacrimal bone and is situated in the medial wall of the orbit. The fossa has two ridges, one anterior called the anterior lacrimal crest and one posterior called the posterior lacrimal crest.

RELATIONS OF THE LACRIMAL SAC

Understanding the anatomical relations of the lacrimal sac is very crucial to understand various lacrimal sac surgeries like the Dacryocystorhinostomy.

Medially it is related to the lacrimal fossa ,the ethmoidal air sinus , middle meatus and nasal cavity.
Laterally it is covered by skin, fascia and the orbicularis muscle.
Anteriorly it is related to the anterior lacrimal crest and the medial canthal tendon .
Posteriorly it has the posterior lacrimal crest and the ethmoid bone

NOTE : MEDIAL PALPEBRAL LIGAMENT covers only the upper part of the sac. Therefore distention of the sac always occurs in the lower part of the sac which is covered by only the orbicularis and skin. Lacrimal abscess and fistula also opens in the lower part owing to the weakness in this area.

An important relation that we must all understand is that with the angular vein. The Angular vein crosses the medial palpebral ligament 8mm from the medial canthus .Many a times a tributary of it passes between it and the medial canthus.Therefore to avoid profuse bleeding during sac surgery, incision should not be made more than 3 mm medial to the medial canthus .

What is NASOLACRIMAL DUCT ?

Let us move on to the next structure in the tear drainage pathway : The NASOLACRIMAL DUCT ( NLD).It is an inferior continuation of the lacrimal sac and opens into the inferior nasal meatus.The direction of NLD is Downwards, backwards and laterally ( can be remembered with a mnemonic DBL).The opening of the duct is partially covered by a mucosal fold (valve of Hasner).

The opening of the NLD is situated about 30- 40 mm from the anterior nares

Its length is 18 mm avg (12-24 mm) and 3 mm in diameter. Size of NLD is smaller in females predisposing them to blockage. Therefore Females are more predisposed to nasolacrimal duct obstruction and dacryocystitis

The NLD has two parts:-

Intraosseous part (12.5 mm): Lies in the nasolacrimal canal formed by the maxilla and the nasal concha.
Intrameatal part (5.5mm) : Lies in the mucous membrane of the lateral wall of the nose.

The image below summarizes the important measurements of the lacrimal apparatus from canaliculus to the nasolacrimal duct.

CLINICAL NUGGET :

Valve of Hasner which prevents the entry of air in to the lacrimal sac when air is blown out of a closed nose.
Canalization of the NLD occurs late in the fetus and in about 30% of infants this is delayed and presents with epiphora and congenital nasolacrimal duct obstruction

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